首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   287篇
  免费   36篇
  国内免费   29篇
  2022年   3篇
  2021年   3篇
  2020年   6篇
  2019年   4篇
  2018年   9篇
  2017年   6篇
  2016年   8篇
  2015年   6篇
  2014年   9篇
  2013年   12篇
  2012年   19篇
  2011年   21篇
  2010年   17篇
  2009年   17篇
  2008年   12篇
  2007年   8篇
  2006年   21篇
  2005年   11篇
  2004年   8篇
  2003年   7篇
  2002年   7篇
  2001年   9篇
  2000年   4篇
  1999年   7篇
  1998年   13篇
  1997年   9篇
  1996年   6篇
  1995年   4篇
  1994年   7篇
  1992年   7篇
  1990年   2篇
  1989年   4篇
  1988年   4篇
  1987年   5篇
  1983年   2篇
  1982年   3篇
  1981年   5篇
  1980年   5篇
  1978年   2篇
  1977年   5篇
  1971年   2篇
  1963年   2篇
  1959年   2篇
  1958年   3篇
  1957年   2篇
  1955年   3篇
  1953年   1篇
  1952年   1篇
  1949年   5篇
  1948年   2篇
排序方式: 共有352条查询结果,搜索用时 15 毫秒
341.
Abstract. Anopheles subpictus Grassi is shown to comprise four reproductively distinct species, designated A, B, C and D, occurring sympatrically in villages of Pondicherry, southeast India.
Adult females were reared individually from wild larvae and examined for their morphological and chromosomal characters. Paracentric fixed inversions on the X-chromosome serve to distinguish the species cytogenetically, with no inversion heterozygotes (i.e. no interspecific hybrids) among totals of 717 species A (X+a,+b), 1863 species B (Xa, b), 869 species C (Xa,+b) and 1365 species D (X +a,b) identified.
Morphologically, diagnostic characters for each of the four species are seen in the egg float ridge number, larval mesothoracic seta 4, pupal seta 7-1 and the palpi of female adults. Species A. C and D immatures inhabit freshwater, whereas the malaria vector species B breeds in saltwater and was found only in coastal villages.  相似文献   
342.
Parental care in mammals is influenced by sensory stimuli from infants, and by changes in the hormone levels of caretakers. To determine the responsiveness to infant cues in nonreproductive adult male common marmosets (Callithrix jacchus) with and without previous experience in caretaking, we exposed 12 males to newborn marmosets and assessed their cortisol plasma levels and behavioral response. Newborn marmosets housed in transparent enclosures were placed inside the cages of the adult male subjects. Males were exposed four times to two different experimental conditions: (a) newborn enclosures remained closed during the observation period and (b) newborn enclosures were opened during the observation period to allow direct social interaction by the adult males. Blood samples from adult males were collected after each behavioral observation trial to measure the levels of cortisol. The behavioral responses of adult males exposed to the closed and open newborn enclosures showed a significant difference only with respect to the frequency of displacements, where males moved among the quadrants of their own cages with greater frequency when the newborn enclosure was sealed. Experienced males approached newborn enclosures more frequently, spent more time in close proximity, and carried and recovered newborns more quickly than inexperienced males. The successive exposure to newborns increased the responsiveness in inexperienced males. The highest levels of plasma cortisol in adult males were recorded following periods of exposure to the sealed newborn enclosures. This suggests that successive exposure to newborns and previous alloparental caregiving experience while living in family groups influences the responsiveness of male marmosets to the sensory cues of newborns. Am. J. Primatol. 75:145‐152, 2013. © 2012 Wiley Periodicals, Inc.  相似文献   
343.
Here we describe a method that allows the isolation of intact trypanosomatid symbionts in amounts sufficient for biochemical analysis. The isolated symbionts retain their characteristic morphological features and are reasonably free of subcellular debris. They actively incorporate [3H]leucine and [35S]methionine into proteins. Chloramphenicol and rifampicin at 50 μg/ml almost completely inhibit the incorporation of protein precursors. The inhibition of protein synthesis by the antibiotics provides direct evidence for the existence of a prokaryotic protein-synthesizing system in this unusual intracellular structure. The pattern of protein synthesis of the isolated symbionts is complex. Several symbiont polypeptides are absent or poorly represented in the flagellate.  相似文献   
344.
Morphological and structural features of the sperm of the Triatoma brasiliensis Neiva, 1911 (Hemiptera: Reduviidae) species complex were examined in this first study investigating the sperm of Heteroptera and the genus Triatoma. Males were dissected and their seminal vesicles removed. For measurement, seminal vesicles were squashed on glass slides, spread, fixed and observed under a photomicroscope. The images were analysed and measures of sperm were made. Data were analysed using one‐way analysis of variance and Tukey's test to detect differentiation among taxa. Furthermore, seminal vesicles were prepared for studies of transmission electron microscopy. All taxa studied showed polymorphic (short and long) sperm. The sperm of Triatoma brasiliensis macromelasoma was significantly longer (in total length) than that of the other four members of the complex, which supports the hypothesis of hybrid speciation of this member of the complex as an increase in the size of typical hybrids under heterosis was previously shown. The sperm cells of the five taxa have similar ultrastructural morphology. The ultrastructural features observed confirm the hypothesis, raised by previous studies, that they are synapomorphic to the suborder Heteroptera.  相似文献   
345.
ADRIAN A. BARNETT  SARAH A. BOYLE  MARILYN M. NORCONK  SUZANNE PALMINTERI  RICARDO R. SANTOS  LIZA M. VEIGA  THIAGO H.G. ALVIM  MARK BOWLER  JANICE CHISM  ANTHONY DI FIORE  EDUARDO FERNANDEZ‐DUQUE  ANA C. P. GUIMARÃES  AMY HARRISON‐LEVINE  TORBJØRN HAUGAASEN  SHAWN LEHMAN  KATHERINE C. MACKINNON  FABIANO R. DE MELO  LEANDRO S. MOREIRA  VIVIANE S. MOURA  CARSON R. PHILLIPS  LILIAM P. PINTO  MARCIO PORT‐CARVALHO  ELEONORE Z. F. SETZ  CHRISTOPHER SHAFFER  LÍVIA RODRIGUES DA SILVA  SULEIMA DO S. B. DA SILVA  RAFAELA F. SOARES  CYNTHIA L. THOMPSON  TATIANA M. VIEIRA  ARIOENE VREEDZAAM  SUZANNE E. WALKER‐PACHECO  WILSON R. SPIRONELLO  ANN MACLARNON  STEPHEN F. FERRARI 《American journal of primatology》2012,74(12):1106-1127
Neotropical monkeys of the genera Cacajao, Chiropotes, and Pithecia (Pitheciidae) are considered to be highly arboreal, spending most of their time feeding and traveling in the upper canopy. Until now, the use of terrestrial substrates has not been analyzed in detail in this group. Here, we review the frequency of terrestrial use among pitheciin taxa to determine the ecological and social conditions that might lead to such behavior. We collated published and unpublished data from 14 taxa in the three genera. Data were gleaned from 53 published studies (including five on multiple pitheciin genera) and personal communications of unpublished data distributed across 31 localities. Terrestrial activity was reported in 61% of Pithecia field studies (11 of 18), in 34% of Chiropotes studies (10 of 29), and 36% of Cacajao studies (4 of 11). Within Pithecia, terrestrial behavior was more frequently reported in smaller species (e.g. P. pithecia) that are vertical clingers and leapers and make extensive use of the understory than in in the larger bodied canopy dwellers of the western Amazon (e.g. P. irrorata). Terrestrial behavior in Pithecia also occurred more frequently and lasted longer than in Cacajao or Chiropotes. An apparent association was found between flooded habitats and terrestrial activity and there is evidence of the development of a “local pattern” of terrestrial use in some populations. Seasonal fruit availability also may stimulate terrestrial behavior. Individuals also descended to the ground when visiting mineral licks, escaping predators, and responding to accidents such as a dropped infant. Overall, the results of this review emphasize that terrestrial use is rare among the pitheciins in general and is usually associated with the exploitation of specific resources or habitat types. Am. J. Primatol. 74:1106‐1127, 2012. © 2012 Wiley Periodicals, Inc.  相似文献   
346.
347.
Infection of carrot roots by Mycocenlrospora acerina in chill storage (3.5 °C) following inoculation with chlamydospores was studied in 1973–74 and 1974–75. AREAS of intact periderm were only rarely infected, and the high level of periderm resistance predominated over other variables. However, wound infection tended to increase with depth of wound and with increasing age of the plants at harvest. Irrespective of age of root or depth of wound, roots were comparatively resistant to infection at harvest and early in storage, resistance being expressed as a restriction of mycelial growth on the wound surface or localisation of the lesion. Increasing susceptibility with time in storage, depth of wounds, or age at harvest, resulted in larger numbers of inoculated sites becoming infected and a more rapid development from localised to progressive lesions.  相似文献   
348.
349.
350.
Meng  X-L; van Dyk  DA 《Biometrika》1999,86(2):301-320
  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号